Thread by @VikiLovesFACS

19,622 ppl tracking #periods, of whom 14,936 receive #CovidVaccine

👉🏻 Dose 1 associated with a 0.7d delay to the next period

👉🏻 Dose 2: 0.6d delay

👉🏻 2x doses in one cycle: 3.91d delay

👉🏻 Back to normal next cycle

👉🏻No change to period length

🧵…

bmjmedicine.bmj.com/content/1/1/e0…

We see these effects with all types of COVID vaccine (mRNA, adenovirus, inactivated virus), suggesting this is likely to be a result of the innate immune response – akin to side effects such as sore arm and fatigue – rather than an effect of any particular vaccine component. 2/

This is in line with previous reports on COVID vaccines, as well as some old reports from other types of vaccine. 3/

theguardian.com/commentisfree/…

This adds to the growing body of evidence that vaccination can cause changes to periods, but these are small compared to natural variation and quickly reverse.

Two reports on this from last winter are summarised here…

4/

bmj.com/content/376/bm…

And here’s my own more recent (little!) study showing the same thing… 5/

https://twitter.com/vikilovesfacs/status/1551526141508419585

The corollary to the finding that vaccine-mediated changes quickly reverse is that if you notice a persistent change, that’s not likely to be vaccine-related so you should get it checked out and treated by a doctor, just as usual. 6/

And if you’re particularly worried about your periods, it’s also important to remember there’s evidence that COVID infection can alter periods – and not necessarily temporarily. Just another reason to avoid getting COVID if you can! 7/

(Links to studies on menstrual changes following COVID infection, since they wouldn’t all fit in one tweet!) 8/

pubmed.ncbi.nlm.nih.gov/34555320/

pubmed.ncbi.nlm.nih.gov/33288478/

pubmed.ncbi.nlm.nih.gov/34308300/

Would I let this put me off getting a dose of COVID vaccine? Well, I’ve been working on this for about 18 months now, and in that time I’ve had dose 2 and a booster, so no!

(I’m likely not to be offered a booster this autumn, but if I am, I’m ‘aving it!) 9/

This is the point at which I usually congratulate the authors, but the eagle eyed will notice I have made a very small contribution to this one myself, so this time I’ll say it’s been a pleasure working with @edelmana1_ae and the team! 10/10